


As Strontium is to Calcium

by consultingsmartass (consulting_smartass)



Category: Sherlock (TV)
Genre: Canon Divergence - The Great Game, Dark John, Dark John Watson, John is Moriarty, M/M, Mildly Dubious Consent, Minor Violence, Secret Identity, animal-human hybrids, jaguar Sherlock, jaguarSherlock, snake John, snakeJohn
Language: English
Status: Completed
Published: 2014-11-10
Updated: 2014-11-10
Packaged: 2018-02-24 20:16:28
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,022
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/2595074
Author URL: https://archiveofourown.org/users/consulting_smartass/pseuds/consultingsmartass
Summary: <blockquote class="userstuff">
              <p>John literally hides his true colours from Sherlock.</p>
            </blockquote>





	As Strontium is to Calcium

**Author's Note:**

  * For [sherlockhasmjolnir](https://archiveofourown.org/gifts?recipient=sherlockhasmjolnir).



> Pinch hit for the Exchangelock ‘What If?’ challenge for sherlockhasmjolnir based on their prompt: “What if John was the real Moriarty?”
> 
> Apologies for the delay in posting this fic (and for it being unbetaed), but the original pinch hitter only handed the prompt off to me about a week ago. As with much of my writing, there is a lot of scientific basis, some of which I have bent and some of which I have utterly bastardized for my own nefarious purposes.

The set of body paint should have been the obvious first clue.

But so many human-snake hybrids utilize it to make their scales appear brighter between moults in order to attract potential mates that Sherlock concludes (incorrectly) that John is feeling insecure.

He _has_ become a bit enamoured of John. It is easy to do, having someone so attentive to his demands and useful on the cases. Not to mention how well John accepted his variety of hybridization from the start. Most people tended to run the other direction (even before he started speaking), wary of the behavioural attributes associated with his other half.

But John had simply looked him up and down once, then offered up his phone without any hesitation. Sherlock had been instantly delighted and intrigued by John’s colourful scales.

“You’re a New World snake hybrid. Which made your time in Afghanistan or Iraq significantly more comfortable than the others in your unit.”

“King snake, actually. And Afghanistan. How'd you–”

“Hmm, are you immune to venom?”

“Can’t say I’ve tried.”

Sensing an exciting new experiment on the horizon, Sherlock had pressed ahead, eager to secure John’s interest in becoming his flatmate. “You should know that I play the violin, prefer solitude most of the time, and sharpen my claws on the furniture when bored.”

“Right. Congratulations?”

“I’ve been told that forewarning flatmates of my apparent idiosyncrasies will increase the likelihood they will remain.”

“Flatmates? Who said anything about that?” John had glanced over at Mike, who made a dismissive grunt and clacked a claw.

“Please, your mere presence screams it.” Sherlock reached over for his coat and returned John’s phone. “I’ve my eye on a flat on Baker Street."

“Wait just a minute. I don’t even know your name. Or what type of cat you are…panther?”

“Jaguar.”

“Aren’t panthers the dark version of jaguars?” asked John, shifting his weight back onto the side not supported by the cane, adding further evidence to Sherlock’s hypothesis that the limp was psychosomatic.

“The appropriate term is ‘melanistic’. And yes. But melanistic leopards are also called panthers, something I find annoyingly imprecise.”

“Melanism – that’s sorta rare, right? Something like less than 10 percent?”

“Six in jaguars. But I still have spots.”

John had squinted then, as if attempting to see them. Sherlock watched his rounded pupils slightly dilate and checked a box in his mental assessment.

And then, to Sherlock’s delight, John’s slightly forked tongue quickly darted in and out, scenting the air. Yes, this was going to work out very well.

  
-

  
The second thing that should have tipped him off was Harry.

Speciation runs in families, meaning that the hybridization in siblings usually tends to be from within the same taxonomic family. Siblings are rarely the exact same species (twins excluded), though they can be from the same genus. So, it was no surprise to anyone that Sherlock was born a human-felid hybrid. Or that his other half was not lion, unlike Mycroft.

Though, the black fur due to the melanism had been a surprise. Other children were quick to tease him, but he was equally quick to snarl and bare his teeth. Now as an adult, Sherlock is secretly pleased that he was not stuck with tawny fur – it would have made stealth in an urban environment impossible.

Sherlock almost instantly deduces that Harry is not serpentine. The phone she gifted to John has a touch screen that is non-conducive to the texture of John’s scaly fingertips, and provides no end of frustration for him, though John is still ridiculously technologically inept besides. No, this particular model is oriented toward amphibian hybrids, of which Sherlock has predicted Harry is closest to a salamander because of the water-absorbing properties of the screen protector. However, this data only means that John either had a different father or he was adopted (the former statistically more likely). Having never met nor seen photos of John’s parents, Sherlock is unable to validate his conclusion, but hardly thinks it necessary. He trusts John, and pursuing that particular line of questioning would probably earn him a low hiss and the silent treatment for the rest of the day (rather like the attempt to learn John's middle name), neither of which he particularly desires.

Deserving John’s attention has become more necessary that Sherlock ever anticipated.

  
-

  
And then there was Sarah. It was an unusual pairing from the start, as avian hybrids were as likely to date snake hybrids as the true animals were to cohabitate in nature. That John would actually court her was odd – odder still was their break-up. Sherlock had decided not to ask after the circumstances of the split after John had spent two days straight under the heating mat in his room.

But Sarah had called him one night weeks later, and in a strangely tight voice tried to convince him that John was not all he seemed.

“Listen, Sherlock. I know you have no reason to trust this information, but please, please don’t be fooled. There’s something…” and here she had trailed off, as if she was hesitant to end the sentence.

“What!?” he had barked, impatient with having to speak on the phone - his ears disliked having something pressed against them.

“He was nearly always late for our dates. Left early, too. Once, I caught him sneaking out of my flat when he was supposed to be spending the night.”

Sherlock had huffed. “Yes, well, I’m certain that it must be difficult for you to handle being considered unattractive and uninteresting company.”

“No!” Sarah insisted, a bit of off-key trill in her voice. “You’ve got it all wrong. He’s–”

“I hardly have time for your weeping. Do _not_ call me again.”

And with that, he’d hung up the phone and deleted the entire unpleasant experience.

-

  
Mycroft had tried to caution him, too.

“There is something peculiar about your doctor,” he had declared during the usual bi-monthly kidnapping.

Sherlock had rolled his eyes and assumed it was jealousy talking. “You find anyone who wants to spend extended periods of time in my presence ‘peculiar’.”

Mycroft’s whiskers had twitched at that. “Must you always be so contrary, brother?”

“Only when you are being particularly annoying.” And sensing a chance to _really_ irritate him, Sherlock had extended his claws and raked them along the luxurious seat cover of Mycroft’s vehicle, splitting the leather. The resulting rumbling growl from Mycroft had been more than satisfying. “Are we done here?”

“Sherlock, this is a pressing issue. I wish you would take me seriously for a change.”

Sighing loudly through his nose, Sherlock had turned away to look out at London’s passing scenery. “I said, are we finished here?”

There was no further sound from behind him. Mycroft had always been better at maintaining detachment.

-

  
Despite all the evidence, it’s only when John’s raspy voice echoes in a darkened swimming pool that Sherlock finally accepts he has made a significant miscalculation.

“Evening.”

Sherlock’s body freezes in place, and he stares over his shoulder in utter disbelief. The memory stick he brought as temptation nearly drops from his fingers as all the messages to his muscles get trapped in his scrambled brain.

“This is a turn-up, isn’t it, Sherlock?”

“John. What the hell ...?” He can barely force his breath through his lips.

“Bet you never saw _this_ coming.”

John’s voice sounds off. Wrong. Lacking the annoyed or fond or placating tone that usually runs through it. The very thing that makes John so…what? Comfortable? Companionable?

His legs push him closer to John even as his stomach feels like it is fleeing in the opposite direction. Sherlock knows his face is giving his inner turmoil away. “How…?”

John scoffs at him in disgust. “You’re supposed to be the greatest mind Britain has to offer, and you didn’t even realize that you were living with the very man you were hunting.”

“John?”

“Wrong-o. James Moriarty, at your service.” John performs a mock bow.

Sherlock’s traitorous brain refuses to superimpose this villainous, sardonic version of John on top of the honourable man he has shared so much with over the months.

And then all the scattered clues from the last few months align. Something from one of his secondary school ecology lectures resurfaces in his memory.

“You’re a reverse mimic. Quite literally. A predator hiding in plain sight,” he manages to stammer out.

A sly smile steals across John’s face. “Took you long enough. Though, if I’d been less careful with my shed skin disposal, you might have had a chance.”

“Body paint. You used body paint to conceal your aggressive mimicry and other half.” The short hair at Sherlock’s nape stands on end, and he unconsciously displays his teeth. “What are you really?”

“Let me guess – you deleted venomous New World snakes. Probably thought it was a waste of ‘space’ on your hard drive, right? Your greatest failing, Sherlock, is that you think you’re so clever.” John laughs at him then, nothing like the warm giggles emitted in the entryway or sitting room, but rather a dry, mocking sound. “I’m a coral snake hybrid – quite venomous. I’m told my bite is extraordinarily painful by those who’ve survived. The rest just scream until the paralysis stops their breathing.”

Sherlock’s ears flatten against his skull instinctively. This is wrong. John is supposed to be his partner, his blogger. Not whatever this is, this bad copy of John.

“How were you able to…?” Realization dawns. “Sarah was your diversion, your decoy.”

“Yes, getting it now, are you? She was a convenient excuse to be away from the flat so I could set other parts of my plan in motion.” John sneers at him. “You think you’re the only one with a network? The only one to use other people to get what you want?”

John takes a few steps forward, bringing them within arm’s distance. “You mammalian hybrids think you’re so much better – more _evolved_ – than the rest of us. Elitist snobs. God, it was a pain to watch you trot around and preen and act superior. And then to have to watch Molly and Lestrade repeatedly kowtow to your ego. Pathetic. For all of you.”

“Like you never had anything to say?” growls Sherlock. “I seem to recall an abundance of verbal accolades spewing from your lips.”

A cruel grin spreads across John’s face, further erasing the memory of the kind man Sherlock has come to respect and need. “Oh, good – finally fighting back. Took you long enough. Through playing the victim, I see.”

“Hardly. Just trying to understand your game. If there’s even one to be played,” Sherlock goads and begins to stalk around John in a counter clockwise motion.

Seemingly unaffected by Sherlock’s pacing, John fires back, “You appeared to enjoy it, though that old woman’s death certainly struck a bit of a soft spot, hmm?

Sherlock refuses to acknowledge John’s thrust, changing topics instead. “How’d you do it? Speak to them while you were standing beside me?”

John rolls his eyes, but continues to follow Sherlock’s circling with his head. “I _told_ you I have people. I mostly prefer to stay above it all. Delegate.”

“And the wounded war veteran backstory – that was a calculated play, too?”

“Obviously, at least, most of it was,” John admits. “How else could I convince you to take me in so I could watch you in action? I admit – it’s far more exciting to see you work in person, when you are desperately trying for my recognition and attention, than from afar or from simple surveillance reports. Of course, they were all I had when I was over in Afghanistan. Simply lovely to have your pictures and comings and goings to peruse at the end of the day.” John leers at him. “I rather enjoyed having such an intimate view of your life.”

“What is it that you want? A flatmate? A nemesis?” Sherlock stops prowling and forces his mind to cycle through all the potential permutations. “An equal?”

“No, Sherlock – I wanted to play. But you’ve turned out to be _such_ a disappointment. Too raw, too needy.” John juts his head forward, and Sherlock fights the instinct to recoil. “Your little speech at Angelo’s made your feelings far too obvious.”

“Speech? You were the one who–”

John sounds angry. “Oh, so quick to defend yourself once again. So predictably _transparent_.”

And then John is completely invading his personal space and Sherlock is so shocked he is frozen on the spot. The quick ‘fsswwwh’ of John’s tongue beside his ear is barely louder than the thumping of his heart.

“Oh, Sherlock, you’ve disappointed me so,” John hisses, each ‘s’ over-emphasized. “I was so certain that you and I would be perfect partners. You should know – I’m rarely wrong.”

Sherlock unfreezes as John grabs the sides of his neck below his ears roughly. He has an arm raised, claws ready to shred, when John surges forward and presses his smooth lips to Sherlock’s. He barely has time to register the unexpected thrust of forked tongue into his mouth before John ends the kiss and rears back. There is a brief moment where Sherlock sees John’s mouth open unnaturally wide, the short fangs within glistening, and then nothing but pain and pressure and blackness.

  
-

  
Sherlock wakes in hospital.

Mycroft is seated nearly, watching him with an expression Sherlock has not seen since he was very young. His mane is uncharacteristically matted and his clothing dishevelled. A glance at the windows tells Sherlock it is night, and a sniff of the air and check of his internal clock allows him to estimate he has been here for approximately 58 hours.

He tries to sit up, but pain instantly shoots through his neck and Sherlock forces himself to relax. The monitors nearby register his distress, but Mycroft does not move and no one else enters the room. Private room with Mycroft-controlled staff, no doubt.

“He bit you, but your fur protected you from the worst of it,” comments Mycroft, lightly.

“Then why does it hurt so badly?” Sherlock grits out, noting that swallowing is exceptionally painful.

Mycroft stands and exaggeratedly stretches. “Despite not injecting you with any venom, which is quite fortunate as antivenin for coral snake bites is quite rare, James Moriarty strangled you until you lost consciousness. You struggled during this process, so his fangs snagged against your neck and narrowly missed your carotid artery. Thirty-nine stitches were needed to close the resulting wounds. Strangely, I received a text from an untraceable number with your location and directions to bring emergency medical assistance.”

“You would have procured the antivenin had I needed it. And I obviously survived being stitched up without any complications, so why are you still here?” Sherlock scrutinizes Mycroft for a moment and then rolls his eyes. “Oh, you’re concerned about my reaction to learning of John’s duplicity.”

Mycroft does not say anything, but that’s answer enough.

“Well,” asserts Sherlock, testing the rotational range of his neck and finding it painfully stiff from the inflammation. “You needn’t be concerned for me, brother. Beyond the initial surprise, I have completely assimilated and accepted this new information.”

“And what do you plan to do about him?” Mycroft sounds disinterested, but the tension in his face says otherwise.

“Hunt him down, obviously.”

“And how do you plan to do that?” Mycroft looks pointedly at his neck, but Sherlock knows he is more interested in the long-term strategy.

“John’s made it clear that he wants to play and that I must become worthy of playing his game.”

“Sherlock, this ‘game’ of yours has already killed dozens–”

Anger rises within Sherlock and he snarls, “Like casualties matter to you.”

Mycroft’s eyes narrow. “But they _do_ matter to you, no matter how you seek to conceal it. And you already perceive John as being one of Moriarty’s casualties, which is exceptionally faulty logic. Surely you are not so clouded by emotion that you cannot see this.”

“I will deal with John as I see fit once I’ve found him and returned the favour.” Sherlock points a claw at his canines. “Although I cannot guarantee that I will not devolve to employing the methods of my other half and just pierce his skull.”

There is no change in Mycroft’s expression. “Indeed.”

“Now get out, Mycroft. I need to rest – I’m in hospital.” Sherlock closes his eyes childishly, hoping it will deter Mycroft from further speech.

But it is a failed tactic. “You are not to leave before your doctor discharges you. I have seen to it that you will be monitored continuously for the duration of your stay.”

Sherlock sighs through his nose. “Fine.”

“They will be reporting to me on your progress and on anything you do to delay or circumvent their treatments.”

“Undoubtedly.”

He can hear Mycroft step closer and resists the instinct to open his eyes. “If you so choose, I am willing to aid in your pursuit of James Moriarty,” promises Mycroft, voice lowered. Sherlock wonders if this is an attempt at emotional manipulation or if Mycroft has the room bugged and does not want to be recorded offering to help Sherlock retaliate. “All you must do is ask.”

And with those final words, Mycroft exits, closing the door behind himself. There is murmuring, presumably with his minder, and then Mycroft’s departing footsteps.

Sherlock waits until the last of Mycroft’s scent has dispelled into the background of hospital smells before opening his eyes once again. The indistinct shape of someone with horns is framed by the door and there is almost no background noise. It is very likely that Mycroft has not only secured this room for him, but the entire floor.

Mycroft’s throwaway comment about receiving a text with Sherlock’s location and orders for medical assistance is now brought to the fore. There is no doubt that it was either sent by John or one of his minions. How intriguing to chase a nemesis who obfuscates with friendship and kisses, while courting with bombs and puzzles.

But Sherlock _will_ pursue John and exact his revenge. It’s only a matter of time and circumstance now.

 

 

 

**Author's Note:**

> Title explanation: Jim Moriarty is to John Watson as strontium is to calcium. Strontium is considered the evil ‘alter ego’ of calcium - it is absorbed by bone tissue in place of calcium and destroys marrow/causes cancer. BUT, if you have just the right amount of strontium, it can act as a strengthener, potentially staving off osteoporosis and tooth decay. So, both calcium and strontium are important/necessary, but too much of the latter can be deadly. (Of course, excess calcium has been found to increase the risk for stroke and heart attack, but I told you at the start that I was going to bend some science…though I have a hard time believing too much John Watson could hypothetically adversely affect Sherlock). *grumbles at the science for ruining the fitting metaphor*


End file.
